This invention relates to strand tension compensation and more particularly to maintaining approximately constant tension in a strand being delivered at an incessant rate and wound upon a package at a varying rate. As used herein, the term "strand" is intended to be construed in its broadest sense and includes any elongated material which may be wound according to the apparatus of the invention. A tension compensator or slackness buffer is provided capable of operating reliably at slow to relatively high speeds.
When a strand is delivered at a constant speed from a stationary source to a conical package, the takeup rate of the package will vary depending upon the point on the package to which the strand is being wound due to the disparity caused by the transverse whether the carrier for the package is straight or conical. This disparity is greater where the carrier is conical because the diameter of the package is smaller at one end than the other, but its angular velocity is constant. When the takeup rate is less than that of the delivery, e.g. when the strand is being wound on the small end of the conical package, excess strand is produced. Concomitant with the production of excess strand are changes in strand tension, which negatively affects strand quality and package formation. Therefore, it has long been considered essential in the textile industry to provide intermediate means of temporarily storing and subsequently releasing excess strand.
Various devices have been developed to attempt to provide this "slackness buffing" action. Most of these devices have employed a spring arrangement whereby a strand engaging member, e.g. a pegged disk or an arm, is biased to store strand when tension is low and release it when tension is high. Devices of this type are shown in U.S. Pat. Nos. 4,133,493, 4,312,482 and 4,605,181. While these mechanisms have proved successful at slow strand delivery speeds, they become inoperative when the otherwise higher speeds are attempted. This is because, at these higher speeds, the mechanical tensioner is operating near its natural frequency which causes catastrophic oscillations. At still higher speeds, the reaction time of the mechanism is inadequate. Therefore, production is impossible at the higher speeds.
Other devices, such as the one shown in U.S. Pat. No. 3,797,775, have attempted to maintain constant tension using a spinning capstan arrangement. Such devices operate by monitoring strand tension and slowing the capstan spin when the tension falls outside of predetermined limits. However, these arrangements have proved unreliable in practice.
Thus, while the above devices do function as slackness buffers to some degree, no apparatus has ever been developed to accomplish this goal reliably up to high delivery speeds.
Accordingly it is an object of this invention to provide an improved strand slackness buffing apparatus capable of operating from low to relatively high speeds.
It is a further object of this invention to provide a strand slackness buffing apparatus using a digital closed loop arrangement for control.